Hot gas defrosting system with gravity liquid return for refrigeration systems



April 11, 1961 J. N. LONG 2,978,877

HOT GAS DEFROSTING SYSTEM WITH GRAVITY LIQUID RETURN FOR REFRIGERATIONSYSTEMS Filed Aug. 4, 1958 I9 25 f o 25 W 3 39 11. z /4 /9 EVAPORATOR l9EVAPORATOR /7 F /5 76 4 /5 30 27 "1" 30 f //9 E 34 I L27 2 6 J5 1 lTRANSFER DRUM OIL 9 l 36 29 comp. SEP. 2 38/ 7 CONDENSER RECEIVER 39INVENTOR. I FUSEPH N .LoNq- M, M ME -77 ftorneys are conventionalsystems.

United States Patent nor GAS DEFROSTING'SYSTEMGRAWTY RETURN FORREFRIGERATION SYS- This invention relatesgenerally. to -refrige-r ationcyatems and more articularly roan improved s stem ot hot gas defrostingfor theevaporator's. s r

'lninefrigeration systems, a considerable amount of ice builds up on theevaporator units and prevents 'prope-r heat transfer, and to insureelfioient operation of the cvaporators, this ice. :buiId-upymustberemoved periodically. i

The principle of using hot gas from the compressor to defrost theevaporators is well known 'and has been used with considerable success.Serious problems have arisen in such defrosting system's, however, theprincipal one. of which is efiiciently disposing of the-large quantityof liquidaformed in the evaporators by condensation' of the hot gas.Stated otherwise, the heat given off 'hy the gaseous refrigerant in athestorage room causes the refrigerant to condense, and. although theevaporator coil or air units have thus been defrosted, aconsiderablequantity ofliquid refrigerantiis formed in the evaporator;whichis-highly undesirable. Y i I The problem of liquid formation in theevaporators hasbeen a troublesome one to the refrigeration industry formany years; Various attempts have been made, both from experimental,andn commercially useful viewpoints, to-dispose; of thisn-l-iquidin randeficient mannen The liquid cannot be returned totheasuctiori "linebecause of consequent damage to ithe co'mpre'ssor.

In accordance with the present invention, a refrigeration system isprovided-having a hotgasdefrosting system in which the liquid thatyiscondensed. in "the evaporator unit: during the defrostingperiodisreturned through a transfer drum :and then directly to thereceiver "bygravity. By means of. thisi-nvention, the necessity of re-evaporating.the liquid asitcomes from thexevaporators andureturning it to thecompressor. is eliminated: :Instead, the

' liquid is returned-more directly-to the receiverandin its usefulliquid state. ASAHJI'CSU'HI, a hot gas def-rosting are rangement fora-refrigerating: system. is provided which is more economical both-toproduce and to-operate. than More specifically, the invention provides adefrosting system of the above typefor use with a pluralityofvevaporator units andwherein an automaticfltimer is used to determinethe defrost time for each evaporator unit or load, so thatthe'defrosting thereof; is accomplished in sequence, one load at a time;1,

Another more specific-object ofthe present invention is to provide anovel electrical control circuiizfor a defrost system of. the abovetypein which th e operation of the evaporator unit or units iscontrolled by their respective temperature controller to maintain room,tempera:

ture under normal operations. The defrosting operation is initiated by.an automatictimer which takes over control of its evaporator from thetemperature controller during the defrosting operation. This automatic,timer actuates other valves to cause-defrosting of the evaporator and insequence if a plurality or evaporators ateus ed in thesystem. l

' 'These and other objects and advantages of the present invention willappear later as this disclosure progresses, reference being had to theaccompanying drawings, 'in which:

Figure its a schematic diagram of one typical' refrigeration systemembodying the improved hot gas defrosting system in accordance with thepresent invention; and

Figure 2 is an electrical Wiring diagram showing the "electricalapparatusand connections involvedin the system of Figure l, thecomponents being in the normal position as when not energized. V

While the invention has been illustrated and described herein as beingadvantageously applicable to a system utilizing two evaporator units; itis not desired or intended to thereby limit the scope or utility of theinvention to any particular number or type of evaporator's. Conventionalair un -s 'or pipe gravity coils may be used,

"for example, as well as-any combination thereof. It is alsocontemplated that descriptive terms employed herein will he given thebroadest: possible interpretation consi'stent wit'lpthe disclosure. l ii 2 Referring "in greater detail-to the drawings, the improvedrefrigeration system includes a conventional compresso'r: 5 having adischarge line 6 which conducts the hot vaporized refrigerant throughthe oil separator 7, check valve 8 andinto the condenser 9. Theli'quidrefriger-ant then leaves the condenser via conduitil'fi which contains ahand Valve 1 1 and enters the high pressure liquid-receiver .12. Thehigh pressure liquid then is dis?- charged firorh the, receiver through:conduit 13, solenoid valves 14. and through the conventionalthermostatic expansion valves 15 where it expands into the evaporatorslo. and 17. The compressor, oil separator, condenser, receiiverandeva'porators are conventional and it will be. understood certainconventional check valves and shut-off valves havebeen omitted, suchasha'nd valves or: each side of the compressor, for the sake of clarityand as their use is Well-known to those skilled in theant. I Asthecontrol valves and switches are the same for each evaporator unit,only one set will, be specifically referredfto but similar referencenumerals will be 'used for similar elements. p t

,During normal operation, liquid refrigerant is admitted totheevaporators when solenoid valves 14 areopehed. After the liquidrefrigerant expands in the evaporator to thereby create the desiredcooling effect in the area. where it' is located, the vaporizedrefrigerant is then permitted tonleave the evaporators via the suctionline 19, when the solenoid valves 20 therein are; opened, and isreturned'to the compressor 5. i p

Solenoid valves 14 and 20 are thus normally operated by the conventionalthermostat, temperature, controller, 22 (Fig. 2) to open and close theliquid line 13 and suction linepl9 to maintain a predetermined:temperature ofthe refrigeratedarea. i

Duringthis normal operation ofthe refrigeration systern, a considerableamount of ice will build up. on the evaporator units and this icemustbe; periodically removed to ,insure good heat transferand efiicientoperationof the units. Prior practice has involved the; peri odicpassing ofthe hot gas from. the compressordirectly into the evaporatorsfor the purpose ofmelting the ice formed thereon. This practice,howevenwhile Sewing to effectively melt the ice, resulted in a largeamount of liquid refrigerant beingformed in 'the evaporators, and'theeflicient disposal of this liquid refrigerant has been a source ofconcerrr tothisjihdustry for many'years. It has been a widespreadpractice to re-evaporate this liquid in one manner or another, asby'me'ans o f 'vari ous h'eat eiichangers', and then ultimately returntheya:

' Inaccordance with the present invention, to initiate a defrost cycle,the hot vaporized refrigerant, or gas, is introduced through conduit 24,which is connected to the compressordiseharge line 6, into' theevaporators when the solenoid valve 25 in line 24 is opened. At the timethis hot gas valve.25 is opened, the-supplyline valve 15 and suctionline valve 19 are closed.

A liquid return line 27 places the evaporator in communication with atransfer drum or tank 29 when the combination relief and solenoid stopvalve 30 in line 27 is open. Valve 30 is set to open at a predeterminedpressure in the evaporators, such as for example, 60 psi.

The valve 30 remains closed during the defrosting period untilthe hotgas in the evaporators causes the pressure therein to rise above thepredetermined pressure relief setting of the valve. The normal pressuresetting (say about 60 psi.) for valve 30, is sufficient to maintainenough heat in the evaporator to cause defrosting.

After approximately 60pounds of pressure has developed in theevaporator, the relief valve 30 opens and this pressure is sufficient,to .force the liquid into the transfer drum, veven if the latter isinstalledin a location above the level of the evaporator. a Ventingmeans'are provided for the drum 29 throng solenoid valve 34 in conduit35, which'conduit connects the upper portion of the drum to the suctionline 19.

During'the defrosting cycle, the solenoid valves 14, 20 are controlledby the defrosting timer 32 rather than by the temperature controller 22.Valves-'25 and 34 are controlledby the timer only and are both openduring the defrosting period as will appear more fully later.

An equalizer line 36 has a solenoid valve 37 therein and places theupper portion of the drum in communication with the condenser. A drainline 38 places the cycle, thereby separating the drum from the highpressure side of the system and the drum is placed under suction 'linepressure by line 35 and open valve 34. Valves 37 and 39 are alsocontrolled only by the defrosting timer 32, as will appear.

After the defrost period has elapsed, as determined by the timer 32, thelatter returns all of the solenoid valves to their normal position. Inother words, the liquid valve 15 and suction valve 19 revert back tocontrol by the thermostat controller 22; hot gas valve 25 and thedrain-relief valve 30 are both closed; equalizing valve 34 to suction isclosed; drain valve 39 and equalizing valve 37 are opened. Under theseconditions, the drum is isolated fromthe low pressure side of the systemand communicates with the high pressure side throughvalves 37 and 39.vAsa result, the pressure then builds up in t conventional type and areactuated by their timer 32;

is a combination control that opens the circuit to shut down the systemin the event the system pressure either exceeds or falls below thepredetermined operating range. The oil pressure control OPC acts to stopthe compressor if its oil pressure fails. The low pressure control LPCis an automatic control that cuts the compressor in and outdepending onthe suction pressure v A manually operated selector switch SS when movedto the H position acts to bypass the LPC switch and the system can thenbe operated by hand or manually. When the selector switch is moved tothe A position, the system operates automatically'under the influence ofthe LPC which turns the compressor on and off in accordance with'thesuction pressure.

The conventional automatic starter S is connected to the three-phasesupply line's bywires50, 51 and 53; to the selector switch SS by wire 54and to the com- .pressor motor CM by wires 55, 56 and'57. j

By means of the present invention, the evaporator units are periodicallyand alternately defrosted by hot gas from the compressor. During the,defrost period for one ,of the units, all of the various solenoidvalves for that unit are controlled by their defrost timer rather thansome of them being controlled by the thermostat control. The liquidformed in the evaporators is released therefrom by the relief' valve,and this liquid is forced under pressure into the transfer drum, whichdrum is,

at that time blocked from the high pressure side ofv the system and isvented to the suction line thereof- After the defrost period isfinished, the timer returns the solenoid valves to their normalposition; that is,.the hot gas is shutoff from the evaporator; theliquid and suction valves revert back. to control by the thermostatController; the transfer drum is placed in communication with the. highpressure side of the system, more specifically, with the condenser andreceiveryand the drum is closed to the low pressure or .suction side ofthe system. The transfer drum is then pressurized andthe'liq uidrefrigerant therein drains by gravity into the high'pres sure receiver,ready for reuse. I

Variousmodes of carrying out'the invention are contemplated as beingwithin the scope of the following erant through a condenser and-receiverand into an These relays have the normally openswitch 41 which,

when closed, energizes valves 37 and 39. The normally closed switch 42,when closed, causes valves 30 and 34 to be energized and open. Thenormally closed switch 43 is connected to the compressor circuit so thatwhen a unit is to be defrosted and its corresponding compressor is'not'operating, the relay cuts the compressor back into the circuit tofurnish hot gas for the defrosting process.

The defrost timers 32 actuate their respective relays 40, control thevalves 25, 34, 37 and 39, and in addition,

during the defrost cycle only, control the solenoid valves Other.conventional controlling devices are shown in Fignrcjand include adualpressure control DPC which evaporator, and also having a suctionlinefor returning evaporated refrigerant back to the compressor, aliquid transfer drum connected between said evaporator and said receiverfor returning liquid refrigerant to said 'receiver, a'hot "gas linebetween the compressor and said evaporator, and temperature responsiveelectrical control means including a defrost timer and valves forregulating refrigerant flow in said systemand adapted to close saidpressure and suction lines and open said hot gas line to thereby permithot gas to enter and defrost said evaporator, said control means alsoadapted to block communication between said drum and receiver and permitliquid refrigerant to pass underpressure from saidevap orator to. saiddrum when pressure in said evaporator exceeds a predetermined amount;and atthe end of the defrost-cycle'said control means being adapted toplace said drum in communication with said receiver and isolate a saiddrum from the suction side of said system whereby liquid refrigerantjcan drain by gravity from the drum to the receiver. r i 1 V,

2. A refrigeration system comprising a compressor having a high pressurerefrigerant line for passing refrigerant through a condenser andreceiver and into an evaporator, and also having a' suction' line forreturning evapdjra ted refrigerant back to the compressor, aliquidtransfer drum connected between said evaporator and said receiver:for

returning liquid refrigerant to said receiver, a vent conduit placingsaid drum in communication with the suction side of the system, a hotgas line between the compressor and said evaporator, and temperatureresponsive electrical control means including a defrost timer and valvesfor regulating refrigerant flow in said system and adapted to (1) closesaid pressure and suction lines and open said hot gas line to therebypermit hot gas to enter and defrost said evaporator, (2) blockcommunication between said drum and receiver and open said vent line,(3) permit liquid refrigerant to pass from said evaporator to said drumwhen pressure in said evaporator exceeds a predetermined amount, and atthe end of the defrost cycle said control being adapted to close saidvent line and place said drum in communication with said receiverwhereby liquid refrigerant can drain by gravity from the drum to thereceiver.

3. In a refrigeration system, the combination comprising a compressor, acondenser, a liquid receiver, an evaporator, a liquid conduit forconnecting said compressor to said evaporator through said condenser andreceiver, a suction conduit connecting said evaporator to saidcompressor for returning refrigerant to said cornpressor, a valve ineach of said liquid and suction conduits, a liquid transfer drum,conduit means between said evaporator and said drum and having acombination electrically operated and pressure relief valve therein, adrain conduit between said drum and said receiver and including a valvetherein, a vent conduit between said drum and the suction side of thesystem and having a valve therein, a hot gas line between the compressorand said evaporator and having a valve therein, and electrical controlmeans adapted at the beginning of a defrosting cycle to close saidliquid, suction and drain conduit valves, and open said hot gas linevalve to thereby permit hot gas to enter and defrost said evaporator,said relief valve being adapted to open when pressure in said evaporatorexceeds a predetermined amount to thereby permit liquid refrigerant topass from said evaporator to said drum, said control means also adaptedat the end of the defrost cycle to place said drum in communication withsaid receiver whereby liquid refrigerant can drain by gravity from thedrum to the receiver.

4. A refrigeration system comprising a compressor, a condenser, a liquidreceiver, an evaporator, a liquid conduit for connecting said compressorto said evaporator through said condenser and receiver, a suctionconduit connecting said evaporator to said compressor for returningrefrigerant to said compressor, a valve in each of said liquid andsuction conduits, a temperature controller for actuating said liquid andsuction conduit valves to thereby control said evaporator during normaloperation, a liquid transfer drum, conduit means between said evaporatorand said drum and having a combination electrically operated andpressure relief valve therein, a drain conduit between said drum andsaid receiver, an equalizer conduit between said drum and saidcondenser, said drain and equalizer conduits each having a valvetherein, a vent conduit between said drum and the suction side of thesystem and having a valve therein, a hot gas line between the compressorand said evaporator and having a valve therein, and electrical controlmeans for actuating said valves and adapted to initiate a defrostingcycle by (1) closing said liquid and suction conduit valves, (2) closingsaid drain and equalizer conduit valves, and (3) opening said hot gasline valve to thereby permit hot gas to enter and defrost saidevaporator, said relief valve being adapted to open When pressure insaid evaporator exceeds a predetermined amount to thereby permit liquid.

refrigerant to pass from said evaporator to said drum, said controlmeans also being adapted at the end of the defrost cycle to isolate saiddrum from the suction side of the system and place said drum incommunication with said receiver whereby liquid refrigerant can drain bygravity from the drum to the receiver.

5. A refrigeration system comprising a compressor, a condenser, a liquidreceiver, an evaporator, a liquid conduit for connecting said compressorto said evaporator through said condenser and receiver, a suctionconduit connecting said evaporator to said compressor for returningrefrigerant to said compressor, a valve in each of said liquid andsuction conduits, a temperature controller for actuating said liquid andsuction conduit valves to thereby control said evaporator during normalrefrigerating operation, a liquid transfer drum, conduit means betweensaid evaporator and said drum and having a combination electricallyoperated and pressure relief valve therein, a drain conduit between saiddrum and said receiver, an equalizer conduit between said drum and saidcondenser, said drain and equalizer conduits each having a valvetherein, a vent conduit between said drum and the suction side of thesystem and having a valve therein, a hot gas line between the compressorand said evaporator and having a valve therein, and electrical controlmeans for actuating said valves for a defrosting cycle and adapted to(1) close said liquid and suction conduit valves, (2) close said drainand equalizer conduit Vales, (3) open said vent conduit valve and (4)open said hot gas line valve to thereby permit hot gas to enter anddefrost said evaporator and place said drum in communication with thesuction side of the system, said relief valve being adapted to open whenpressure in said evaporator exceeds a predetermined amount to therebypermit liquid refrigerant to pass from said evaporator to said drum,said control means also adapted at the end of the defrost cycle to closesaid vent conduit valve and open said valves in said drain and equalizerconduits, to thereby place said drum in communication with saidcondenser and receiver and isolate said drum from the suction side ofsaid system whereby liquid refrigerant can drain by gravity from thedrum to the receiver.

References Cited in the file of this patent UNITED STATES PATENTS2,525,560 Pabst Oct. 10, 1950 2,729,950 Toothman Jan. 10, 1956 2,770,104Sweynor Nov. 13, 1956 2,778,195 Christensen J an. 22, 1956 2,841,962Richards July 8, 1958

